What is needed beyond the typical knife making equipment?
Should I go ahead and buy a rise/fall indicator now if I decide to sign up?
I don't use one personally, some people like them, personally, I built one, but never use it. I find it easier to simply get it close, and then "adjust by feel". I haven't seen Daniel much lately, I moved across town so can't get out there as often as I'd like, but last I checked, he was in the same boat.
The most important tools for building nice slipjoints, at least, the way I build them, are;
a) a good precision drill press, or a mini mill for drilling holes. I don't have a mini-mill, and I don't like them for milling, but they make nice little drill presses. Personally I've got a couple of Hamilton Vari-Matics, and a few Vigor/Grobet Optical drills (high speed, ultra precision, small capacity bench drills), for poking holes.
b) a surface grinder (very few top end slipjoint makers that I know, don't have and use one, yes it's possible, but it's a lot more tedious, and requires a lot more patience, or a lower standard for fit and finish)
c) a horizontal grinder (almost every serious folder maker I know has and uses a dedicated horizontal, there's just too much work that is really difficult to do if you can't grind in this orientation, and/or square up something with a tool rest at exactly 90 degrees to the platen or wheel)
d) a disc grinder (this is optional, but everybody I know that has one, won't give it up for folder work. You can square and flaten much easier on this than any belt grinder, although you need a tool rest also)
If you've got a disc, or are really patient with lapping, and start with precision ground stock, you can maybe get away without a surface grinder, but the moment you use one, you won't want to live without one, and you'll be perpetually feeling like you're fighting shit you shouldn't have to, when you don't.
If you've made other folders, you've probably got much of this stuff, and a good start on making slipjoints. They can of course, be made with much less equipment, but these tools can really help getting everything to come together correctly. You've got tons of tiny interactions from various parts that each contribute to the overall being right or wrong, when you nail it together.
Personally, I'm a big proponent of full sized knee mills, and have two in the shop (a Bridgeport, and a much larger K&T vertical), however, I never use a mill for slipjoint work except to cut integral bolsters. I do however, use the surface grinder on each one.
Yes a SG attachment with a TW-90 will work, but I personally don't find belts and contact wheels as accurate as I'd like for this task. If you assume that you're getting everything perfectly flat/parallel because you're using an "SG" and get a nice finish, you may find yourself fighting stuff. Really flat and really parallel are crucial to slipjoint precision, and it's much easier to achieve with a real SG and stones as opposed to belts. However, Daniel uses a belt converted SG, and gets results he's happy with on it.